Regeneration of photographic bleach/fix baths

ABSTRACT

Depleted photographic bleach/fix baths which include bleaching agents (such as the iron III complex of ethylenediaminetetraacetic acid) and a silver halide solvent are regenerated by addition to a recycled stream thereof of an iron, cobalt and copper-free regenerating solution which includes a polycarboxylic acid, a silver halide solvent, and an organic bleach-enhancing compound which includes at least one atom which is different from carbon, hydrogen and nitrogen.

United States Patent 1 Newman et al.

[ Oct. 23, 1973 REGENERATION OF PHOTOGRAPHIC BLEACH/FIX BATHS [75]Inventors: Norman Newman; Richard S. Fisch,

both of St. Paul, Minn.

[22] Filed: Dec. 15, 1971 [21] Appl. No.2 208,434

[52] US. Cl. 96/50 A, 96/50 R, 96/60 R,

96/60 BF [51] Int. Cl G03c 5/26, G03c 5/32 [58] Field of Search 96/60,60 BF, 50 A [56] References Cited UNITED STATES PATENTS 3,619,18811/1971 Alcock et al. 96/60 Cooley 96/60 Ohi et a1. 96/60 BF PrimaryExaminer-Norman G. Torchin Assistant ExaminerM. F. KelleyAttorney-Kinney, Alexander, Sell, Steldt & Delahunt [57] ABSTRACTDepleted photographic bleach/fix baths which include bleaching agents(such as the iron lIl complex of ethylenediaminetetraacetic acid) and asilver halide solvent are regenerated by addition to a recycled streamthereof of an iron, cobaltand copper-free regeneratingsolution whichincludes a polycarboxylic acid, a silver halide solvent, and an organicbleach-enhancing compound which includes at least one atom which isdifferent from carbon, hydrogen and nitrogen.

12 Claims, No Drawings REGENERATION OF PHOTOGRAPHIC BLEACH/FIX BATHS Thepresent invention relates to silver halide photographic processing andmore particularly relates to the regeneration of bleach/fix photographicprocessing baths.

Bleach baths and bleach/fix baths have long been employed in thephotographic processing of silver halide photographic materials,particularly color materials, to oxidize free silver images to silverhalide and to remove silver halide from the materials. Early bleachbaths employed an alkali metal ferricyanide bleaching agent which wasreduced to a ferrocyanide during the bleaching (silver oxidation)reaction. Although such bleach baths met with great success, they werefound to contribute greatly to pollution. Ferricyanide-free bleachlfixbaths which employ bleaching agents such as the iron Ill complex ofethylene-diaminetetraacetic acid reduce pollution problems, and havegained wide popularity. In this type of bleach/fix bath, a bleachingagent, which may be exemplified as the iron IIIethylenediaminetetraacetic acid complex, is reduced to the iron IIcomplex during the silver-bleaching reaction. Such bleach/fix baths alsoinclude a silver solvent (fixing agent) such as sodium thiosulfate(hypo), a source baths. A method for the regeneration of bleach/fix ofsulfite ion (as an antioxidant), and various other photographicadditives such as wetting agents, etc.

Referring to iron III ethylenediaminetetraacetic bleach/fix bath asexemplary of ferricyanide-free bleach/fix baths, it will be understoodthat during the bleaching and fixing reactions, the concentrations ofthe various bath ingredients change greatly. For example', during thebleaching reaction, iron III is reduced to iron II, the concentration ofiron III being reduced. The concentration of silver halide solvent whichis available for dissolving or complexing with silver halide is likewisereduced, and the concentration of silver (e.g., as thesilver-thiosulfate complex), and of halides increases. Such changes inthe bleach/fix bath composition reduce both bleaching and fixing rates,producing depleted baths. To avoid this problem, one may replenish sucha bath by adding thereto an aqueous replenisher composition whichcontains the necessary chemicals to maintain the working bleach/fix bathat a working strength. Overflow which results from the addition of thereplenisher composition may be descarded or may be re-used by theaddition thereto of chemicals necessary to form the replenishercomposition. Normally, the overflow is desilvered (e.g., by passagethereof through steel wool), and the iron. I] complex thereof isoxidized to the iron III complex by, for example, bubbling airtherethrough. The chemicals added to the thus-treated overflow willnormally contain ethylenediaminetetraacetic acid to replace theethylenediaminetetraacetic acid which is required to complex with theiron released into the solution during the 'desilvering operation.Particularly when photographic materials having unusually largequantities of I silver therein are processed through such bleach/fixbaths,

replenishment of the baths must take place at an increasingly rapid ratein order to maintain the concentration of iron llI complex, silverhalide solvent, and the like, so that rapid bleaching and fixing may bemaintained. In some instances, replenishment cannot practically becarried out at a sufficiently rapid rate to maintain the correct balanceof chemicalsin the bleach/fix baths which would permit such baths tooperate with a reduced replenishment rate and at lower concentrationlevels of silver halide solvent (e. g., hypo) and bleaching agent (e.g.,iron lII complexes), and at higher silver levels, is greatly to bedesired.

It is thus an object of the present invention to provide a process forthe regeneration of photographic bleach- /fix baths which permits areduced replenishment rate.

It is another object of the invention to provide a regeneratingcomposition which may be added to depleted photographic bleach/fix bathsfor regeneration thereof.

In one embodiment thereof, the present invention relates to animprovement in the process for regeneration of a depleted photographicbleach/fix bath which contains a bleaching agent selected from the groupconsisting of ferric, cobaltic and cupric complex salts of an acidselected from the group consisting of polycarboxylic acids,hydroxypolycarboxylic acids and aminopolycarboxylic acids, and a silverhalide solvent, the process comprising desilvering and oxidizing awithdrawn portion of the bleach/fix bath and then returning thewithdrawn portion to the bleach/fix bath. The improvement comprisesadding to the withdrawn portion of the bath an iron, cobalt andcopper-free regenerating composition which includes a silver halidesolvent, said acid of said bleaching agent, and an organicbleach-enhancing compound which includes at least one atom which isdifferent from carbon, hydrogen and oxygen.

Although the regeneration composition referred to above may be suppliedin solid form, it has been found desirable to provide this compositionas a ready-made aqueous solution which may be added to the withdrawnportion of the bleach/fix bath and the whole diluted with water ifdesired to provide a replenisher solution which may then be added to thebleach/fix bath. Accordingly, in another embodiment the presentinvention relates to a regenerating composition for regeneratingdepleted photographic bleach/fix working baths which contain a bleachingagent selected from the group consisting of ferric, cobaltic and cupriccomplex salts of an acid selected from the group consisting ofpolycarboxylic acids, hydroxypolycarboxylic acids andaminopolycarboxylic acids, and a silver halide solvent; whichregenerating composition (preferably in solution form) is essentiallyfree 'of metals which, in complex form, may participate in the silverbleach (redox) process, such as iron, cobalt and copper, and whichincludes a silver halide solvent, said acid of said bleaching agent, andan organic bleach-enhancing compound which includes at least one atomwhich is different from carbon, oxygen and hydrogen.

As used herein, bleach-enhancing compound" refers'to an organic compoundwhich includes at least one atom which is different from carbon,hydrogen and oxygen (e.g., sulfur, nitrogen, selenium) and which iscapable of enhancing (e.g., accelerating) the rate of bleaching of asilver image in a photographic element treated with a bleach/fix bath towhich has been added the compound. Selection of bleach-enhancingcompounds of the invention is facilitated by the following test:

A gelatino silver halide photographic element which contains 50milligrams per square decimeter of silver is exposed uniformly to lightand is developed in a suitable developer to convert all of the silverhalide to metallic silver, and is then washed thoroughly with water. Thedeveloped element is then divided into two portions. The first portionis placed in a bleach/fix bath of the following composition for 1%minutes at 88F.:

Sodium ferric ethylenediaminetetraacetic acid 80 g. Disodiumethylenediaminetetraacetic acid 30 g. Sodium sulfite (anhydrous) g.Ammonium thiosulfate (60% aqueous solution) 200 ml.

pH: adjusted to 7.0 by addition of sodium hydroxide or sulfuric acid.

To a second 1 liter solution of the above-identified bleach/fix bath isadded 5 grams of a candidate bleachenhancing compound, and the secondportion of the developer silver halide element is immersed therein at88F for 1% minutes. After withdrawal of the developed silver halideelements from the bleach/fix baths, the elements are thoroughly washedwith water and the quantity of silver therein is measured by X-Rayfluorescence by the method reported in Automatic Direct Reading X-RaySpectroscopy Applied to the Determination of Silver, AnalyticalChemistry, Vol. 35, No. 1, January, 1961. A reduction (e.g., of aboutpercent or more) in the amount of residual metallic silver in thedeveloped silver halide element which was treated in the bleach/fix bathcontaining the candidate compound indicates that this compound is abbleach-enhancing" compound as referred to herein.

Preferably, the bleach-enhancing compounds of the invention are organiccompounds which include at least one sulfur atom in a thiocarbonyl group(e.g., as in thiosemicarbazide, thiourea, thiocarbohydrazide, etc.); ina thioether group (e.g., as in thio derivatives of polyoxyethylene,etc.); or in a sulfonium group (e.g., as in thionine, 1,6-hexylenedimethylsulfonium dibromide, etc.); or include at least one nitrogenatom in a quaternary ammonium group (e.g., ethylpyridinium chloride,alkyl-, aryland cyclo-alkyl pyridinium salts, etc.); or include at leastone selenium atom in a selenocarbonyl group (e.g., as in selenourea,selenosemicarbazide, etc.) Most preferably, the bleach-enhancingcompounds of the invention include both sulfur and nitrogen atoms in athioamide group, such as in thiosemicarbazide, thiourea andthiocarbohydrazide, and derivatives thereof such as the alkyl, aryl,cycloalkyl, aralkyl, and heterocyclic derivatives thereof as disclosedin Swiss Pat. No. 336,257 and British Pat. No. 1,150,466.Thiosemicarbazide is most preferred.

It has surprisingly been found that the present invention permitsbleach/fix baths of the type described herein to be operated atsignificantly lower concentrations of bleaching agent complex and ofsilver halide solvent available for use (e.g., hypo), and atsignificantly higher concentrations of silver (e.g., as thethiosulfate-silver complex). Accordingly, the rate at which the workingbleach/fix bath need be charged with replenisher solution issignificantly reduced.

As used herein, overflow refers to portions of spent bleach/fix bathwhich are removed from the system. After discarding a portion of theoverflow, the remainder is combined, either continuously or in separateportions, with the regenerating composition referred to above resulting(after optional dilution with water) in a replenisher solution. As willbe understood, the rate at which the replenisher solution is supplied tothe working bleach/fix bath will be controlled so as to maintain theconcentration of ingredients in the bleach/fix bath at a level whichpermits essentially complete bleaching to be obtained in a relativelyshort amount of time (e.g., within about 1 minute at 88F.). Further, theconcentration of ingredients in the regenerating composition, and theratio of regenerating composition to the retained overflow may also bedetermined by simple experimentation. It has been found that aconcentration of bleach-enhancing compound in the replenisher solutionof from about 0.25 to about 10.0 grams per liter will yield acceptableresults, although from about 0.5 to about 5.0 grams per liter ispreferred.

The bleaching agents employed in the present invention are selected fromthe group consisting of ferric, cobaltic and cupric complex salts of anacid selected from the group consisting of polycarboxylic acids,hydroxypolycarboxylic acids and aminopolycarboxylic acids (includingnon-complex salts of such acids, such as the ammonium and alkali metal(e.g., sodium and potassium) salts thereof). Examples of such bleachingagents are the iron Ill complex salt of ethylenediaminetetraacetic acid,sodium salt, the cobalt lll complex salt of nitrilotriacetic acid, theiron 11] complex salt of ethylenediamine hydroxyethyltriacetic acid; thecopper ll disodium complex salt of iminodiacetic acid; copper Ildisodium complex salt of dipicolinic acid, the 3-hydroxy glutaric acidamino cobalt complex (as in British Pat. No. 777,635), and the iron Illcomplex salt of malonic acid.

The regenerating compositions of the present invention include the acidof the bleaching agent; that is, if the iron Ill salt ofethylenediaminetetraacetic acid is employed in the bleach/fix workingbath, then ethylenediaminetetraacetic acid will ordinarily be employedin the regenerating composition.

Silver halide solvents which are useful in the present invention includesources of thiosulfate ion (e.g., sodium thiosulfate), sources ofthiocyanate ion (such as sodiumthiocyanate), thioglycollic acid and thelike. Such materials are commonly referred to as fixing agents" and arewell known in the photographic art (see US. Pat. No. 2,748,000). Inaddition, the regenerating compositions of the invention may includesuch standard photographic additives as surfactants, oxidationinhibitors (e.g., sulfite ion precursors such as sodium sulfite),hardeners such as aluminum chloride UV. absorbers and the like.

As noted above, the regenerating compositions of the present inventionare free of iron, cobalt and copper, which metals form complex saltswith polycarboxylic acids, hydroxypolycarboxylic acids, andaminopolycarboxylic acids. During the desilvering process, withdrawnportions of overflow may be passed through, for example, iron or coppergauzes, resulting in the deposition of silver thereon and the releasetherefrom of iron or copper ions. If the bleaching agent of thebleach/fix working bath is an iron 111 complex, then desilverization maybe accomplished by use of an iron material such as steel wool.Similarly, if a cupric complex salt is employed as a bleaching agent,then a copper material such as gauze may be used for desilverization.

The invention may be more clearly understood by reference to thefollowing illustrative, non-limiting example:

EXAMPLE Silver halide color print paper having three silver halide,coupler-containing layers sensitized to different regions of thespectrum, which contained in total milligrams of silver (as silverhalide) was uniformly exposed to white light and thereafter wascontinuously processed in a processing sequence which consisted of 5development in a paraphenylenediamine type color photographic developersolution, treatment in a bleach/fix working bath (see infra), waterwash, treatment in a stabilizing bath at pH 3.8, water rinse and drying.The bleach/fix working bath consisted of 600 ml. of a solution havingthe following composition:

Sodium ferric ethylenediaminetetraacetic acid 80 g. Disodiumethylenediaminetetraacetic acid 30 g. Sodium sulflte (anhydrous) l0.g.Ammonium thiosulfate (60% aqueous solution) 200 ml. Water to I000 ml.

pH: adjusted to 7.0 by addition of sodium hydroxide or sulfuric acid.

In order to maintain a proper balance of chemicals in the path duringcontinuous processing of the color print paper, a replenisher solutionwas continuously supplied to the bath. The resulting overflow from thebath was collected, desilvered by passage through steel wool, andoxidized by bubbling air therethrough. Onefifth of the volume thereofwas described. To the remaining four-fifths of the desilvered andoxidized overflow was added a regenerating composition (in aqueoussolution form) of the following composition:

Disodium ethylenediaminetetraacetic acid 6.5 g. Sodium sulfite 3.5 g.Ammonium thiosulfate (60% aqueous solution) 45 ml. Water to 160 ml.

The regenerating composition was added in a volume ratio of one partthereof to five parts of retained overflow solution, the resultingsolution being made up with water to a volume of 1.25 times the volumeof the retained overflow. The resulting replenisher solution was thenused to continuously replenish the working bleach/fix bath. The rate atwhich the replenisher solution was continuously added to the workingbleach/fix bath was controlled so as to assure complete bleaching of thesilver image on the color print paper which was complete bleaching ofthe color print paper, only 28.6 milliliters of the resultingreplenisher solution was required to be added per square foot of colorprint paper.

We claim:

. 1. In the process for regeneration of a depleted photographicbleach/fix bath which contains a bleaching agent selected from the groupconsisting of ferric, cobaltic and cupric complex salts of an acidselected from the group consisting of polycarboxylic acids,hydroxypolycarboxylic acids and aminopolycarboxylic acids, and a silverhalide solvent, which process comprises desilvering and oxidizing awithdrawn portion of said bath and then returning said withdrawn portionto said bleach/fix bath, the improvement which comprises adding to saidwithdrawn portion an iron, cobalt, and copper-free regeneratingcomposition which includes a silver halide solvent, said acid of saidbleaching agent, and an organic bleach-enhancing compound which includesat least one atom which is different from carbon, hydrogen or oxygen.

2. The process according to claim 1 wherein said bleach-enhancingcompound is thiosemicarbazide.

3. The process according to claim 1 wherein said bleach-enhancingcompound is thiocarbohydrazide.

4. The process according to claim 1 wherein said bleaching agent is iron(Ill) complex of ethylenediaminetetraacetic acid.

5. The process according to claim 1 wherein said bleaching agent is theiron (lll) salt of nitrilotriacetic acid. t

6. The process according to claim 1 wherein said regeneratingcomposition is in aqueous solution form.

7. A regenerating composition for regenerating depleted photographicbleach/fix working baths which contains a bleaching agent selected fromthe group consisting of ferric, cobaltic and cupric complex salts of anacid selected from the group consisting of polycarboxylic acids,hydroxypolycarboxylic acids and aminopolycarboxylic acids, and a silverhalide solvent, said composition being essentially free of iron, cobaltand copper and including a silver halide solvent, said acid of saidbleaching agent, and an organic bleachenhancing compound which includesat least one sulfur or at least one nitrogen atom.

8. The composition of claim 7 wherein said bleachenhancing compound isthiosemicarbazide.

9. The composition of claim 7 wherein said bleachenhancing compound isthiocarbohydrazide.

l0. Thecomposition of claim 7 wherein said bleaching agent is iron (III)complex of ethylenediaminetetraacetic acid.

11. The composition of claim 7 wherein said bleaching agent is the iron(III) salt of nitrilotriacetic acid.

12. The composition of claim 7 wherein said composition is in aqueoussolution form.

2. The process according to claim 1 wherein said bleach-enhancingcompound is thiosemicarbazide.
 3. The process according to claim 1wherein said bleach-enhancing compound is thiocarbohydrazide.
 4. Theprocess according to claim 1 wherein said bleaching agent is iron (III)complex of ethylenediaminetetraacetic acid.
 5. The process according toclaim 1 wherein said bleaching agent is the iron (III) salt ofnitrilotriacetic acid.
 6. The process according to claim 1 wherein saidregenerating composition is in aqueous solution form.
 7. A regeneratingcomposition for regenerating depleted photographic bleach/fix workingbaths which contains a bleaching agent selected from the groupconsisting of ferric, cobaltic and cupric complex salts of an acidselected from the group consisting of polycarboxylic acids,hydroxypolycarboxylic acids and aminopolycarboxylic acids, and a silverhalide solvent, said composition being essentially free of iron, cobaltand copper and including a sIlver halide solvent, said acid of saidbleaching agent, and an organic bleach-enhancing compound which includesat least one sulfur or at least one nitrogen atom.
 8. The composition ofclaim 7 wherein said bleach-enhancing compound is thiosemicarbazide. 9.The composition of claim 7 wherein said bleach-enhancing compound isthiocarbohydrazide.
 10. The composition of claim 7 wherein saidbleaching agent is iron (III) complex of ethylenediaminetetraaceticacid.
 11. The composition of claim 7 wherein said bleaching agent is theiron (III) salt of nitrilotriacetic acid.
 12. The composition of claim 7wherein said composition is in aqueous solution form.